In design of high efficiency compressors, it is important to provide relatively unrestricted suction gas flow to the compressor. However, this suction process results in the generation of substantial noise due both to the rapid flow of suction gas into the compressor as well as the operation of the intake valving. Accordingly, it is desirable to provide some form of noise attenuating means in the suction gas flowpath. The use of various forms of restrictors and baffles in the main flowpath of the suction gas is undesirable in that such devices may create excessive flow losses requiring that larger conduits be utilized to prevent compressor suction starvation.
Present practice requires the design of compressors to be as compact as possible. The available space within the assembly thus imposes several constraints on the size of suction mufflers. Further, because of these space limitations, it is often necessary to extend the suction gas conduit in close proximity to the discharge muffler and conduits. The discharge gas is relatively hot due to the compression process and in order to maintain a high volumetric efficiency, it is desirable to minimize heat transfer from the discharge gas to the suction gas.
Accordingly, the present invention provides a refrigeration compressor having an improved suction gas muffler which effectively attenuates noise generated from the above-mentioned sources while still enabling relatively free unrestricted flow to the compressor.
The suction gas muffler of the present invention is similar to the suction muffler described in assignee's U.S. Pat. No. 5,129,793 with the exception of the incorporation of a step located on the internal diameter of the suction gas muffler. The step on the internal diameter of the muffler increases the size of the internal diameter in the direction of flow of the suction gas. This stepped internal diameter of the suction gas muffler produced dramatic performance improvements with no sound penalty. This surprising improvement in performance is the result of changes in various factors including: the acoustic characteristics of the suction process; pressure waves from the head are restricted from moving against the gas flow towards the motor cover; and the suction pressure wave is brought more in phase with the piston motion thus reducing the suction work required.
The suction gas muffler of the present invention is of the side branch type and comprises a relatively large diameter stepped conduit having a housing secured thereto which defines a pair of side branch chambers each of which may be tuned to a different fundamental frequency. A pair of longitudinally spaced openings provide communication with each of the respective chambers and serves to define an impedance tube therebetween which may be tuned to attenuate a third fundamental frequency. Integrally formed baffles and ribs within each of the chambers further aid in noise attenuation by reducing standing waves within the chambers as well as enhancing the rigidity of the muffler. The muffler is preferably fabricated from a polymeric composition so as to minimize heating of the suction gas being supplied to the compressor. Further, the use of such materials enables the suction conduit and muffler to be very inexpensively fabricated by suitable forming means such as, for example, injection molding.
Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings.